The objective of the proposed studies is to identify the critical molecular events that direct specific repression of PRL gene expression. Aim 1 is to establish the importance of the alternative splice form of Pit-1 in the repression of PRL and to determine the molecular events that contribute to the splice choice. Aim 2 is to determine if specific DNA elements in the PRL gene are the key determinants of why PRL gene expression is inhibited in GH3 cell-induced tumors, while GH gene expression is not. Aim 3 will be to examine the interaction of proteins with the PRL and GH promoters, and to characterize the proteins that are involved in the specific repression of the PRL gene.